March 16, 2009 From mundane traffic overpasses to marvelous feats of soaring engineering, bridges are something we tend to take for granted - until something goes wrong that is. A team from the University of Michigan is leading a five-year, $19 million project to engineer an intelligent infrastructure monitoring system designed to prevent tragedies like the collapse of the Interstate 35 West bridge over the Mississippi river in 2007 in which 13 people were killed and 145 were injured.
The I 35 collapse was said to be caused by a design fault with additional weight being the contributing factor in its collapse. The American Society of Civil Engineers in their ‘Report Card for America’s Infrastructure’ have given the bridges in the US (and there are some 600,000 of them) a ‘C’ for 2009, which is a passing grade but not exactly praiseworthy, especially when you might possibly be driving over the one in four that are said to be “structurally deficient or functionally obsolete.”
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The planned UM inspection system consists of four types of sensors that detect cracks, erosion or any signs of weakness and relay information to a bridge inspector wirelessly through the Internet and enhanced antennas. This will greatly enhance the current manual bridge inspection which relies largely on the human eye and hopefully, prevent any more collapses.
Of the four types of new sensors, one is a new type of high-performance concrete that has been engineered to be ‘bendable’ and conduct electricity. On the bridges to be tested, the decks will be replaced with this new concrete and any changes in the electrical conductivity will signal weaknesses.
A “sensing skin” that is carbon nanotube-based will also be glued or painted onto any places that may be significant to the bridge’s integrity, it will detect any cracks or corrosion that would otherwise have been invisible to the bridge inspector’s eye.
The third sensor is a series of low-cost nodes that measure damage responses like strain and changes in vibration. They are low-powered with the ability to harvest energy from the bridge vibrations or radio waves. The last type of sensor would placed on vehicles traveling the bridge itself to gauge the bridge’s reaction to the strain it imposes on the infrastructure, meaning the effects of heavy trucks on bridges could be measured for the first time.
"Our work will add to what is currently done, not replace it," said Research Professor Tim Gordon, head of UMTRI's Engineering Research Division. "The infrastructure problem and the feasibility of new monitoring strategies are emerging at the same time. We believe we have ways of testing the performance of bridges as integrated structures, not just inspecting their components."
The system will be tested on several test bridges whose locations are not yet determined and eventually the University plans to commercialize the system.